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From Jim Jagielski <...@jaguNET.com>
Subject Re: svn commit: r1696960 - in /httpd/httpd/trunk: CHANGES docs/log-message-tags/next-number modules/proxy/mod_proxy_balancer.c
Date Tue, 25 Aug 2015 13:59:09 GMT
When 1st configured, Apache sees how many balancers there are
set in the config file. It then pads that amount by growth to
allow for the to-be-added dynamic addition of new balancers via
the balancer manager (ala adding members).

The assumption is that if the actual config file is changed,
then the runtime configuration of balancers and members
is no longer valid; after all, if someone is changing the
config file, they could have done the same to add/change
bal/mem settings. So a config file change means something
more "serious" at which point the dynamic config should be
considered void and Apache starts with a clean (dynamic) slate
and just uses what's in the config only.

> On Aug 25, 2015, at 9:48 AM, Yann Ylavic <ylavic.dev@gmail.com> wrote:
> 
> Hm, what's the point of the balancers and balancer->workers growth margin then?
> The first time the configration is loaded we create enough room for
> adding new balancers/workers, and on (graceful) restart we wouldn't
> use this space?
> That's also how the balancer-manager works when adding a new worker to
> a balancer, AFAICT.
> 
> 
> On Tue, Aug 25, 2015 at 3:43 PM, Jim Jagielski <jim@jagunet.com> wrote:
>> You mean via changing the config file? If so, then all bets
>> are off. You change the config file and restart then Apache
>> should start off w/ a clean slate. Even so, you need to handle
>> freeing the old shared mem segment and creating a brand new one
>> with the "correct" size... Trying to "use" the old one is
>> just fraught with issues.
>> 
>> 
>>> On Aug 25, 2015, at 9:15 AM, Yann Ylavic <ylavic.dev@gmail.com> wrote:
>>> 
>>> Well, if one adds a new balancer before restarting, at post_config
>>> time conf->balancers->nelts is +1 wrt the previous load...
>>> 
>>> On Tue, Aug 25, 2015 at 2:46 PM, Jim Jagielski <jim@jagunet.com> wrote:
>>>> But the number of balancers does not change yet... And when it
>>>> is implemented the overall size of the storage slot should *never*
>>>> change. It must be constant, ala the scoreboard.
>>>> 
>>>>> On Aug 25, 2015, at 8:39 AM, Yann Ylavic <ylavic.dev@gmail.com>
wrote:
>>>>> 
>>>>> At every startup, in balancer_post_config:
>>>>>  conf->max_balancers = conf->balancers->nelts + conf->bgrowth;
>>>>> 
>>>>> which means that if you add a balancer and restart, storage->create()
>>>>> (eg. slotmem_create) will try to find an existing slot with this ID
>>>>> and the exact ALIGNED_PROXY_BALANCER_SHARED_SIZE * conf->max_balancers
>>>>> size, and fail:
>>>>>  if (apr_shm_size_get(shm) != size) {
>>>>>      apr_shm_detach(shm);
>>>>>      ap_log_error(APLOG_MARK, APLOG_ERR, 0, ap_server_conf, APLOGNO(02599)
>>>>>                   "existing shared memory for %s could not be used
>>>>> (failed size check)",
>>>>>                   fname);
>>>>>      return APR_EINVAL;
>>>>>  }
>>>>> 
>>>>> By using storage->attach() first (which is based on the ID only and
>>>>> returns the existing item_size and item_num), we can do the check
>>>>> ourselves and fail only if conf->max_balancers > item_num, allowing
>>>>> for balancers to be added thanks to growth margin used at startup.
>>>>> 
>>>>> On Tue, Aug 25, 2015 at 2:12 PM, Jim Jagielski <jim@jagunet.com>
wrote:
>>>>>> How and when do ALIGNED_PROXY_BALANCER_SHARED_SIZE and conf->max_balancers
>>>>>> change???
>>>>>> 
>>>>>>> On Aug 21, 2015, at 8:34 AM, ylavic@apache.org wrote:
>>>>>>> 
>>>>>>> Author: ylavic
>>>>>>> Date: Fri Aug 21 12:34:02 2015
>>>>>>> New Revision: 1696960
>>>>>>> 
>>>>>>> URL: http://svn.apache.org/r1696960
>>>>>>> Log:
>>>>>>> mod_proxy_balancer: Fix balancers and balancer members reuse
on
>>>>>>> restart when new ones are added.  PR 58024.
>>>>>>> 
>>>>>>> Since slotmem_create() issues a strict check on the size of an
existing
>>>>>>> slot before reusing it, it won't reuse existing balancers and
members when
>>>>>>> new ones are added during restart (whereas growth margins would
allow it).
>>>>>>> Fix this by using slotmem_attach() first and if it succeeds do
the checks
>>>>>>> based on the returned previous number of existing entries.
>>>>>>> 
>>>>>>> Modified:
>>>>>>> httpd/httpd/trunk/CHANGES
>>>>>>> httpd/httpd/trunk/docs/log-message-tags/next-number
>>>>>>> httpd/httpd/trunk/modules/proxy/mod_proxy_balancer.c
>>>>>>> 
>>>>>>> Modified: httpd/httpd/trunk/CHANGES
>>>>>>> URL: http://svn.apache.org/viewvc/httpd/httpd/trunk/CHANGES?rev=1696960&r1=1696959&r2=1696960&view=diff
>>>>>>> ==============================================================================
>>>>>>> --- httpd/httpd/trunk/CHANGES [utf-8] (original)
>>>>>>> +++ httpd/httpd/trunk/CHANGES [utf-8] Fri Aug 21 12:34:02 2015
>>>>>>> @@ -1,6 +1,9 @@
>>>>>>>                                                       -*- coding:
utf-8 -*-
>>>>>>> Changes with Apache 2.5.0
>>>>>>> 
>>>>>>> +  *) mod_proxy_balancer: Fix balancers and balancer members
reuse on
>>>>>>> +     restart when new ones are added.  PR 58024.  [Yann Ylavic]
>>>>>>> +
>>>>>>> *) mod_socache_memcache: Add the 'MemcacheConnTTL' directive
to control how
>>>>>>>   long to keep idle connections with the memcache server(s).
>>>>>>>   Change default value from 600 usec (!) to 15 sec. PR 58091
>>>>>>> 
>>>>>>> Modified: httpd/httpd/trunk/docs/log-message-tags/next-number
>>>>>>> URL: http://svn.apache.org/viewvc/httpd/httpd/trunk/docs/log-message-tags/next-number?rev=1696960&r1=1696959&r2=1696960&view=diff
>>>>>>> ==============================================================================
>>>>>>> --- httpd/httpd/trunk/docs/log-message-tags/next-number (original)
>>>>>>> +++ httpd/httpd/trunk/docs/log-message-tags/next-number Fri Aug
21 12:34:02 2015
>>>>>>> @@ -1 +1 @@
>>>>>>> -2964
>>>>>>> +2966
>>>>>>> 
>>>>>>> Modified: httpd/httpd/trunk/modules/proxy/mod_proxy_balancer.c
>>>>>>> URL: http://svn.apache.org/viewvc/httpd/httpd/trunk/modules/proxy/mod_proxy_balancer.c?rev=1696960&r1=1696959&r2=1696960&view=diff
>>>>>>> ==============================================================================
>>>>>>> --- httpd/httpd/trunk/modules/proxy/mod_proxy_balancer.c (original)
>>>>>>> +++ httpd/httpd/trunk/modules/proxy/mod_proxy_balancer.c Fri
Aug 21 12:34:02 2015
>>>>>>> @@ -761,8 +761,11 @@ static int balancer_post_config(apr_pool
>>>>>>>      char *id;
>>>>>>>      proxy_balancer *balancer;
>>>>>>>      ap_slotmem_type_t type;
>>>>>>> +        apr_size_t attached_size;
>>>>>>> +        unsigned int attached_num;
>>>>>>>      void *sconf = s->module_config;
>>>>>>>      conf = (proxy_server_conf *)ap_get_module_config(sconf,
&proxy_module);
>>>>>>> +
>>>>>>>      /*
>>>>>>>       * During create_proxy_config() we created a dummy id. Now
that
>>>>>>>       * we have identifying info, we can create the real id
>>>>>>> @@ -794,11 +797,39 @@ static int balancer_post_config(apr_pool
>>>>>>>                       (int)ALIGNED_PROXY_BALANCER_SHARED_SIZE,
>>>>>>>                       (int)conf->balancers->nelts, conf->max_balancers);
>>>>>>> 
>>>>>>> -            rv = storage->create(&new, conf->id,
>>>>>>> -                                 ALIGNED_PROXY_BALANCER_SHARED_SIZE,
>>>>>>> -                                 conf->max_balancers, type,
pconf);
>>>>>>> +            /* First try to attach() since the number of configured
balancers
>>>>>>> +             * may have changed during restart, and we don't
want create() to
>>>>>>> +             * fail because the overall size * number of entries
is not stricly
>>>>>>> +             * identical to the previous run.  There may still
be enough room
>>>>>>> +             * for this new run thanks to bgrowth margin, so
if attach()
>>>>>>> +             * succeeds we can only check for the number of
available entries
>>>>>>> +             * to be *greater or* equal to what we need now.
 If attach() fails
>>>>>>> +             * we simply fall back to create().
>>>>>>> +             */
>>>>>>> +            rv = storage->attach(&new, conf->id,
>>>>>>> +                                 &attached_size, &attached_num,
>>>>>>> +                                 pconf);
>>>>>>> +            if (rv != APR_SUCCESS) {
>>>>>>> +                rv = storage->create(&new, conf->id,
>>>>>>> +                                     ALIGNED_PROXY_BALANCER_SHARED_SIZE,
>>>>>>> +                                     conf->max_balancers,
type, pconf);
>>>>>>> +            }
>>>>>>> +            else {
>>>>>>> +                ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, s,
APLOGNO(02964)
>>>>>>> +                             "Balancers attached: %d, %d (%d)",
>>>>>>> +                             (int)ALIGNED_PROXY_BALANCER_SHARED_SIZE,
>>>>>>> +                             (int)attached_num, conf->max_balancers);
>>>>>>> +                if (attached_size == ALIGNED_PROXY_BALANCER_SHARED_SIZE
>>>>>>> +                        && attached_num >= conf->balancers->nelts)
{
>>>>>>> +                    conf->max_balancers = attached_num;
>>>>>>> +                }
>>>>>>> +                else {
>>>>>>> +                    rv = APR_ENOSPC;
>>>>>>> +                }
>>>>>>> +            }
>>>>>>>          if (rv != APR_SUCCESS) {
>>>>>>> -                ap_log_error(APLOG_MARK, APLOG_EMERG, rv, s,
APLOGNO(01179) "balancer slotmem_create failed");
>>>>>>> +                ap_log_error(APLOG_MARK, APLOG_EMERG, rv, s,
APLOGNO(01179)
>>>>>>> +                             "balancer slotmem create or attach
failed");
>>>>>>>              return !OK;
>>>>>>>          }
>>>>>>>          conf->bslot = new;
>>>>>>> @@ -864,11 +895,32 @@ static int balancer_post_config(apr_pool
>>>>>>>                       (int)ALIGNED_PROXY_WORKER_SHARED_SIZE,
>>>>>>>                       (int)balancer->max_workers, i);
>>>>>>> 
>>>>>>> -            rv = storage->create(&new, balancer->s->sname,
>>>>>>> -                                 ALIGNED_PROXY_WORKER_SHARED_SIZE,
>>>>>>> -                                 balancer->max_workers, type,
pconf);
>>>>>>> +            /* try to attach first (see rationale from balancers
above) */
>>>>>>> +            rv = storage->attach(&new, balancer->s->sname,
>>>>>>> +                                 &attached_size, &attached_num,
>>>>>>> +                                 pconf);
>>>>>>> +            if (rv != APR_SUCCESS) {
>>>>>>> +                rv = storage->create(&new, balancer->s->sname,
>>>>>>> +                                     ALIGNED_PROXY_WORKER_SHARED_SIZE,
>>>>>>> +                                     balancer->max_workers,
type, pconf);
>>>>>>> +            }
>>>>>>> +            else {
>>>>>>> +                ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, s,
APLOGNO(02965)
>>>>>>> +                             "Workers attached: %s (%s), %d,
%d (%d) [%u]",
>>>>>>> +                             balancer->s->name, balancer->s->sname,
>>>>>>> +                             (int)ALIGNED_PROXY_WORKER_SHARED_SIZE,
>>>>>>> +                             (int)attached_num, balancer->max_workers,
i);
>>>>>>> +                if (attached_size == ALIGNED_PROXY_WORKER_SHARED_SIZE
>>>>>>> +                        && attached_num >= balancer->workers->nelts)
{
>>>>>>> +                    balancer->max_workers = attached_num;
>>>>>>> +                }
>>>>>>> +                else {
>>>>>>> +                    rv = APR_ENOSPC;
>>>>>>> +                }
>>>>>>> +            }
>>>>>>>          if (rv != APR_SUCCESS) {
>>>>>>> -                ap_log_error(APLOG_MARK, APLOG_EMERG, rv, s,
APLOGNO(01185) "worker slotmem_create failed");
>>>>>>> +                ap_log_error(APLOG_MARK, APLOG_EMERG, rv, s,
APLOGNO(01185)
>>>>>>> +                             "worker slotmem create or attach
failed");
>>>>>>>              return !OK;
>>>>>>>          }
>>>>>>>          balancer->wslot = new;
>>>>>>> 
>>>>>>> 
>>>>>> 
>>>> 
>> 


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